floop 2.1.4

Dynamic values and animation API for Flutter widgets. Change values from anywhere and widgets are rebuild automatically. Transition values with one function call to animate a widget.

Floop

Animation API and dynamic values for Flutter widgets. Allows building interactive apps using purely Stateless Widgets. Inspired by react-recollect.

How to use

• Add with Floop at the end of the widget class definition
• Retrieve a value from floop and the widget will reactively update on changes to it

Extra step:

• Use transition(ms) within the build method to have a value transition from 0 to 1 in ms milliseconds.

Example:

-class Clicker extends StatelessWidget {
+class Clicker extends StatelessWidget with Floop {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // Text widget always displays the current value of #clicks.
      body: Center(
        child: Opacity(
          opacity: transition(2000),
          child: Text('${floop[#clicks]}'),
        )
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () {
          // Change #clicks from anywhere in the app (except build methods).
          floop[#clicks]++;
          // Control transitions using [TrasitionGroup] methods.
          TransitionGroup(context: context).restart();
        }),
      ),
    );
  }
}

Other options:

• [DynamicWidget] is a Floop widget that carries it's own state in the form of a map of dynamic values.
• ... extends StatelessWidget with Floop is equivalent to ... extends FloopWidget.
• ...extends StatefulWidget with FloopStateful or extend ... extends FloopStatefulWidget for stateful widgets.
• Maps of dynamic values like floop can be instantiated using [DynMap].

Suggested use cases

• Store data that affects many widgets (eg. user data).

• Asynchronous operations like data fetching. Conditionally check floop['myData'] == null ? LoadingWidget() : DisplayDataWidget(floop['myData']).

• Animate widgets.

Install

Add floop dependency to the project's pubspec.yaml

depedencies:
  floop:

Run flutter pub get in the root directory of the project.

Transitions and Animations

All floop widgets can be animated using [transition], which returns a [double] that will go from 0 to 1 in the specified time:

@override
Widget build(BuildContext context) {
  return Opacity(
    opacity: transition(3000), // transitions a number from 0 to 1
    child: Container(
      Text('Text will completely appear after 3 seconds')),
  );
}

Transitions of the same refresh periodicity are synchronized.

[TransitionGroup] controls transitions. They can be resumed, reversed, time shifted, paused, restarted or canceled. [transitionOf] retrieves values. [transitionEval] receives an evaluate function as parameter. It cannot be used inside build methods. Provide a key parameter to be able to reference them from inside build methods (using [transitionOf]). [TransitionsConfig] to set default parameters.

Special Considerations

Builders

Dynamic values do not work inside [Builder] functions. A workaround is to read the dynamic values outside of the builder definition. Example:

Works fine:

  @override
  Widget build(BuildContext context) {
    final opacity = transition(3000);
    final text = floop[myText];
    return Builder(
      builder: (context) => Opacity(
        opacity: opacity,
        child: Container(
          Text(text),
      );
    );
  }

Should not do:

@override
Widget build(BuildContext context) {
  return Builder(
    builder: (context) => Opacity(
      // Error.
      opacity: transition(3000),
      child: Container(
        // The widget will not update if floop[myText] changes.
        Text(floop[myText])),
    );
  );
}

The builder function is a callback that executes outside of the encompassing Floop widget's [build] method and Floop does not listen to these builds.

Transitions and Keys in Stateless Widgets

Use keys on widgets that invoke [transition] when the widgets belong to the same list of children widgets ...children: [widget1, widget2,...], and this list can change. These are the same conditions when keys should be used on Stateful widgets.

Details

DynMap

floop is an instance of [DynMap], which implements [Map]. Other instances can be created in the same way as any map is created, e.g: Map<String, int> myDynInts = DynMap().

Widgets subscribe to the values retrieved during their last build.

Maps and Lists

[Map] and [List] values are not stored as they are when using []= operator, they get deep copied. Every [Map] gets copied as a [DynMap] instance, while lists get copied using [List.unmodifiable]. This behavior ensures that either the values cannot be changed or if they change, the changes will be detected to update elements accordingly. Maps and lists can still be stored as they are by using the method [DynMap.setValue]. This method also receives optional parameter to prevent triggering updates to widgets.

Initializing and Disposing a Context

[Floop.initContext] is invoked by an [BuildContext] instance when it's added for the first time to the element tree.

[Floop.disposeContext] is invoked by an [BuildContext] instance when it's unmounted (removed from tree to never be used again).

These methods are the equivalent to [State.init] and [State.dispose]. They can be overriden to initialize or dispose dynamic values.

Performance

Performance rules of thumb:

• Including [Floop] on a widget is less impactful than wrapping a widget with another widget.
• Reading one value from floop inside a build method is like reading five [Map] values

The only impact Floop has on a widget is to its build time and it does not go beyond x1.2 on minimal widgets (a container, a button and a text).

These build time increases can be considered as rough references when comparing reading data from a [DynMap] in Floop widgets, to reading the same data from a [LinkedHashMap] in widgets without Floop. Only integer numbers were used as keys and values. It was also assumed that the same context would access the same keys on every invocation to [StatelessWidget.build]. It's more expensive when there are different keys read (that should be an uncommon case).

On small Widgets (less than 10 lines in the build method), including Floop implies these build time performance hits:

• x1.15 when 0 values are read.
• x1.9 when up to 5 values are read.
• x2.9 when up to 20 values are read.

On medium Widgets:

• x1.1 when 0 values are read.
• x1.6 when up to 5 values are read.
• x2.5 when up to 20 values are read.

[DynMap] in comparison to a regular [LinkedHashMap]:

Reading:

• x1.1 using the map like a regular map (outside build methods).
• x3 while Floop is on 'listening' mode (when a Widget is building).
• x5 considering the whole preprocessing (start listening) and post processing (stop listening).

Writing:

• x1.6.

Collaborate

Writing code, reporting bugs, giving advice or ideas to improve the library is appreciated.